All of the female hormones interact with your cells through estrogen receptors. There are all kinds of estrogen receptors in your body, each with unique "assignments." Brain receptors control temperature (hot flashes), memory, sleep, and concentration. Bone receptors determine bone mass and strength. Breast receptors are responsible for breast cell growth.

Tamoxifen is probably the best understood of the breast cancer-fighting compounds that target the estrogen receptor. Tamoxifen works by blocking the estrogen receptors on the breast tissue cells and slowing their estrogen-fuelled growth.

Tamoxifen has added estrogen-like benefits, keeping bones strong and cholesterol down. It also produces unwanted side effects. Some women who take tamoxifen experience hot flashes brought on by the drug's influence on the brain's temperature control center, and studies have shown a slightly increased risk of endometrial cancer with long-term use.